Conventionally, various products in the shape of particles are produced by processing resins depending on the properties thereof. For example, disclosed is a method for producing a toner as one example of particles, in which a composition including a resin and additive is melted and kneaded, followed by cooling, solidification, pulverization, and classification (see PTL 1). In the case where a toner is produced by the aforementioned method, however, fine powder generated by pulverization is mixed in the toner, and therefore basic properties of the toner, such as charging properties, fixing ability, and heat resistant storage stability, are impaired.
As for a method for producing a toner without pulverizing a resin or the like, disclosed is a method for emulsifying and dispersing a colorant resin solution (see PTL 2). In according to this method, a colorant resin solution containing a polyester-based resin, a colorant, and a water-insoluble organic solvent is emulsified and dispersed in water to form an O/W emulsion, followed by removing the organic solvent to color resin particles, which are then aggregated to produce toner particles. In the case where a toner is produced in this method, however, there is a problem that a large load is applied to the environment as the organic solvent is used.
As for a method for producing a toner without using an organic solvent, disclosed is a method using liquid carbon dioxide (see PTL 3). In accordance with this method, a resin melt of polyester and liquid carbon dioxide are mixed by a static mixer, and the obtain mixture is discharged from a nozzle provided at an edge of the static mixer into the atmosphere having the temperature of 20° C. under the atmospheric pressure, to expand the mixture due to the reduction in the pressure, to thereby produce a toner.
In case of granulation through a one-fluid nozzle, however, a particle size distribution becomes broad, as a melted resin and a compressive fluid, such as liquid carbon dioxide, are mixed and the mixture of low viscosity is jetted from the nozzle, and therefore there is a problem that it is difficult to produce a large quantity of particles having uniformly small diameters.